The present invention relates to gas-solid separation. More particularly, the present invention relates to a method for removal of entrained solids from gases in upright cyclone separators and especially in cyclone separators useful in separating entrained solid catalyst from hydrocarbon vapors or flue gases encountered in the catalytic cracking of hydrocarbon.
This method is used in cyclone separators widely used as dust collectors or gas-solid separators. For example, cyclones are widely used in both the reactor and regenerator sections of Fluidized Catalytic Cracking Units (FCCU) for the removal of entrained catalyst particles from hydrocarbon effluent vapors and flue gases used and/or produced in the cracking process. The construction and operation of cyclone separators is well known to those skilled in the art. Briefly, a cyclone separator has a cylindrical upper portion, commonly called a barrel, adjoined to a lower conic section, the lower, smaller diameter end of the conic section forming a solids outlet. Gas enters the barrel portion, tangentially, at one or more points, and exits through a centrally disposed gas outlet extending through the top wall of the barrel. The dust, e.g. catalyst particles, by virtue of their inertia, tend to move toward the outside walls of the separator and eventually leave through the solids outlet. Essentially, a cyclone separator is a settling chamber in which gravitational acceleration is replaced by centrifugal acceleration. Under common operating conditions, it is not unusual for the centrifugal separating force or acceleration to be several hundred times gravitational force. The higher forces imparted to the dust or solid particles results in a highly erosive effect on the internal walls of the cyclone thereby resulting in rapid wearing. Likewise, a too high of velocity of the catalyst particles causes excessive grinding up of the catalyst to dust, resulting in loss of catalyst. Cyclone separators of the type under consideration are commonly used as last stage dust collectors, as for example, to remove remaining dust and solid particles from gases such as flue gases prior to atmospheric venting. Because of increasing concern for the environment, it is necessary that such cyclone separators, when they are used as last stage solids removing devices, be as efficient as possible in order that the gas vented to the atmosphere will be as pollution free as possible.